Recent progress of technology in various fields of industries such as electric and electronic field, fields of office automation (OA) and audiovisual (AV) devices, automobile industries, etc., is amazing, and the polymeric materials used in these new fields of art are required to have high performance such as high strength and high thermal resistance that could not be realized with the conventional polymeric materials and the excellent functions such as those of a thermoplastic elastomer with excellent thermal resistance that could not be attained with the conventional polymeric materials.
Request for such high performance and enhanced functional characteristics has been dealt with by various methods in the respective fields of application. For instance, in the case of thermoplastic resins, strenuous studies have been made on the development of condensation type polymers represented by engineering plastic, development of whole aromatic polymers, blending of these polymeric materials, etc. In the case of thermosetting resins, too, similar studies have been made in accordance with the field of use.
Presently, as thermoplastic elastomer (hereinafter referred to as "TPE"), TPE's comprising block copolymers composed of soft segments and hard segments are widely used.
As such TPE, there are known the block copolymers called polyester elastomers consisting of the aliphatic polyether portion such as polytetramethylene glycol and the polyester portion such as polyethylene terephthalate and polybutylene terephthalate, and the block copolymers called polyamide elastomers consisting of the aliphatic polyether portion and the polyamide portion such as polydodecalactum. It is considered that in these block copolymers, each of the hard segments constitutes a micro-domain structure, which plays the role of physical crosslinking point to provide rubber elasticity to said copolymers.
European Patent Laid-Open Specification 0287233 discloses preparation of a polymer solution for coating from a copolymer having an aromatic polyester as side chain, that is, a copolymer having an aromatic polymer covalently bonded to an acrylic or polyester resin, said polymer solution being claimed to be capable of forming a coating film with high hardness. This patent specification, however, is silent on the aromatic oligomer of the present invention.
Further, the whole aromatic polyesters, such as polyhydroxybenzoic acid, are the polymers with excellent thermal resistance but the scope of their use is limited due to the problems that they are not thermoplastic, that they are insoluble in solvents, etc. It is tried, therefore, to lower the melting temperature by random copolymerization with other copolymerizable monomers or to improve solubility in solvents.
However, studies of these polymeric materials with high performance and high functional ability from the stage of synthesis require a long time and also involve many economical problems. Also, in certain fields of use, the two conflicting properties, viz. high thermal resistance and excellent moldability, are required at the same time, but it is hard to develop a polymeric material which can satisfy this requirement. Further, attempts have been made to realize high performance by blending the polymeric materials, but in many cases such attempts would fail to attain the target performance due to the reasons such as difficulty of morphological control.
In TPE comprising a copolymer composed of soft segments and hard segments, the ratio of the hard segments needs to be not less than several 10% by weight for allowing them to constitute a micro-domain structure and play the role of physical crosslinking point. Also, these TPE are large in compression set (100.degree. C., 70 hr) and not so high in thermal resistance. This is because the hard segment itself does not have high thermal resistance.
Further, there is yet available no report on use of an aromatic polyester as starting material of TPE by lowering the molecular weight of the polyester to make it fusible.